70. Climbing Stairs.java

/*
You are climbing a staircase. It takes n steps to reach the top.

Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?

 

Example 1:

Input: n = 2
Output: 2
Explanation: There are two ways to climb to the top.
1. 1 step + 1 step
2. 2 steps
Example 2:

Input: n = 3
Output: 3
Explanation: There are three ways to climb to the top.
1. 1 step + 1 step + 1 step
2. 1 step + 2 steps
3. 2 steps + 1 step
 

Constraints:

1 <= n <= 45
*/


//Solution:

class Solution {
    public int climbStairs(int n) {
        if(n == 1) return 1;
        int num1 =1,num2=1;
        int sum = 0;
        for(int i = 1;i<n;i++){
            sum = num1 + num2;
            num2 = num1;
            num1 = sum;
        }
        return sum;
        
    }
}